1. Field of the Disclosure
The present invention relates to gas filling apparatus and particularly, but not exclusively, to gas filling apparatus for filling insulated glass units (double glazing units) with an inert gas such as argon.
2. Technical Background
Insulated glass units have traditionally comprised two or more panes of glass, with each pair of panes separated by a peripheral spacer bar. The spacer bar has a moisture absorbing element to absorb any moisture in the air in the unit.
The thermal efficiency of insulated glass units can be further improved by inserting an inert gas, typically argon as it relatively inexpensive, in the unit. In the case of very large scale production runs, this can be achieved by automated assembly of the panes and spacer bars in an inert gas. However, the size and expense of the plant required means that this is only possible for the very largest producers of such units.
As an alternative to assembling the panes and spacer bars in an inert atmosphere, the panes and spacer bars can be assembled in air in the traditional manner, with the spacer bar being provided with one or more apertures through which an inert gas can be subsequently introduced and the air removed. One technique for doing this uses two apertures, one at the top of the unit and one at the bottom of the unit with the inert gas being filled through the bottom and the air expelled through the top (the gas being denser than air). The air being expelled through the top of the unit is monitored and when the percentage of inert gas in the air exceeds a predetermined threshold, the filling process is terminated and the apertures are plugged.
An alternative method utilises a single aperture in the spacing bar at the top of the cavity, through which a nozzle of a lance is inserted. This nozzle can be in the form of a coaxial pipe which can both introduce the gas and remove the air. Again, the concentration of gas in the air leaving the unit can be monitored and filling terminated when the gas content exceeds a predetermined threshold.
One gas filler for filling an insulated glass unit in the manner described above is the IGA 200, manufactured by the present applicant. This controls the gas flow to the lance and monitors the percentage of gas in the air returning from the unit.
Filling may be commenced by operation of a start button on the unit and is terminated by the unit detecting the gas in the return air flow is above a predetermined concentration. Typically, an operator will be filling many units and to assist the operator a foot peddle is available to control the dispensing of the gas.
Insulated glass units, depending on their size and the flow rate of gas, may take a minute or more to fill and therefore a single operator may control two or more lances. Gas filling machines are available which have two or more lances, such as the IGA 60, manufactured by the present applicant. Each lance may be controlled by a separate foot peddle, however it is difficult for a single operator to operate more than two lances, for confusion can occur regarding the stage of operation of a particular lance and this may result in units being incorrectly filled.